Firewall
A firewall is a hardware or software device intended to prevent unauthorized users from either accessing, or sending data from, a private local area network or a single PC, usually connected to the Internet.
Although dial-up users are generally safe from security breaches, thanks to dynamic IP allocation (where a dial-up user receives a different IP address every time they connect to their ISP), users with fixed IP's or always-on connections (DSL and Cable modem users, for example) are vulnerable. To prevent unauthorized access to a network or individual PC, or service interruptions from DoS (denial of service) attacks, firewalls restrict access by allowing only authorized communications to pass through.
Each network device uses a dedicated port on a PC. Email uses one port, telnet another, http another. By default, Windows leaves 65,000 ports wide open. Firewalls close unneeded/unused ports and filter the ports that are utilized.
To find out if your PC or network is vulnerable, visit these sites to run security tests:
To protect a PC or network with a software firewall:
Reviews of a few hardware firewalls and routers:
